I am thinking of making a poster Titling it something like "help me make you sound great " showing proper mic holding ,not to point the mic at the monitor etc. what do you think ?
General:
Do hold the mic close, almost touching your lips, but don't try to "eat" it.
When shouting or screaming, move the mic away from your mouth.
Don't "cup" the mic with your hands.
Don't "swing" the mic by its cable (if wired).
Wireless microphone:
"Budget" wireless mics have a very sloppy companding circuit that destroys dynamics and creates massive amounts of distortion. There is nothing you can do to improve that.
An "acceptable" wireless is going to cost upwards of $400/channel. I never hand a $400 wireless to a drunk. I have different cabled mics to switch out, depending on my judgement of the prospective singer.
There are a lot of pretty good wired mics for $100-$150. Keep some "throw-aways" handy for when you sense you need them.
... Read this:
http://cdn.shure.com/publication/upload/838/microphone_techniques_for_live_sound_reinforcement_english.pdf-Dennis